A city-wide telepoint system based on second generation cordless telephony (CT-2) technology provides service within small isolated "islands of coverage", each defined by a limited radio coverage range provided by one or more stationary communication units, e.g., base units or base stations, located therein. Cordless telephone handset units (CT handsets) are portable communication transceiver units, e.g., portable radiotelephone transceivers, that can access the public switched telephone network (PSTN) via any accessible base unit within communication range. Each base unit typically can handle one or more independent communications with one or more CT handsets, respectively, over a limited number of adjacent communication channels. A public telephone booth, or base unit, can support up to twelve to sixteen simultaneous conversations at the same location.
Each independent communication between a CT handset and a base unit utilizes full duplex burst transmission communication over a single channel. The base unit transmits a burst of information for a predetermined time interval, e.g., for one millisecond, while the CT handset receives the transmitted information. Then, for the next predetermined time interval, e.g., for the next millisecond, the CT handset transmits its burst of information and the base unit receives the transmitted information. This pulsed transmission exchange of information allows full duplex communication, e.g., a telephone conversation, over a single radio frequency (RF) channel.
Although the CT-2 protocol provides synchronization of the exchange of information between a base unit and a CT handset, i.e., one transmits while the other receives, multiple communications between "nearby" base units and CT handsets may not be synchronized with each other. Due to a limited number of available communication channels, some of the communications may be in very close or adjacent channels. Unsynchronized transmits and receives between two or more very close or adjacent communication channels can result in substantial interference between the respective communications because of the limited adjacent channel selectivity of the communication units and the wide band technology utilized in the front end of the transceivers, in both the base units and the CT handsets. Depending on how far the channels are apart, this interference can destroy the conversations, or it can introduce spurious "clicks" and "pops".
One approach to synchronize the time division duplexing communications between the multiple base units and CT handsets has been to interconnect the base units with wire and provide a 500 Hz synchronization signal, e.g., a 2 millisecond duty cycle square-wave signal, therebetween. Typically, a "master" base unit has supplied the synchronization timing signal to all the "slave" base units in a defined coverage area. In this way, all the base units would "burst" transmit at the same time, and then receive at the same time. The CT handsets, being synchronized by the CT-2 protocol with their respective base units, would likewise receive when the base units were transmitting and would transmit when the base units were receiving.
Regrettably, this approach has a number of drawbacks. First, wire interconnection between all the "nearby" base units is not always possible due to competitive systems being in close proximity. Second, limitations in the logistics available in certain situations can preclude physical wire interconnection between base units. Third, the additional wiring adds to the overall system cost and complexity which is a competitive disadvantage. Consequently, due to the very competitive nature of cordless radiotelephone communication systems, such as CT-2 systems, a better solution to this problem is necessary.